Field of the Disclosure
Embodiments of the present application relate to the art of a shift control system for an automatic vehicle transmission configured to change a speed ratio stepwise.
Discussion of the Related Art
When the vehicle is accelerated, upshifting is executed to reduce a speed ratio as a result of an increase in a vehicle speed. In this case, a speed of a prime mover such as an engine is reduced while increasing an output of the engine and hence a driving force is changed significantly by the upshifting. Especially, given that the upshifting is executed by a clutch-to-clutch shifting, the drive force would be changed significantly to generate a shock as a result of disengaging a clutch engaged to establish the previous gear stage and engaging another clutch to establish the higher gear stage. JP-A-2010-115983 describes a controller for vehicle powertrain configured to compensate for torque drop by a motor or an engine during a torque phase in the clutch-to-clutch shifting. To this end, according to the teachings of JP-A-2010-115983, a torque compensating rate is determined based on a result of experimentation, and a timing of execution of the torque compensation is learnt. Specifically, if the learning of the timing is not progressed, the torque compensating rate is reduced.
JP-A-2007-239832 describes a controller for an automobile having a feedback means that controls a torque transmitting capacity of a clutch involved in a shifting operation of a transmission based on a difference between a target speed and an actual engine speed. In addition, JP-A-2001-124196 describes a shift control device of automobile configured to correct an engine torque during execution of a power-on downshifting. According to the teachings of JP-A-2001-124196, the control device calculates excess and deficiency of energy based on a difference between a target value and an actual value of an input speed during execution of the power-on downshifting, and corrects the engine torque in accordance with the calculated excess or deficiency of energy.
According to the teachings of JP-A-2010-115983, the torque compensating rate is determined based on a result of experimentation. However, given that an internal combustion engine is used as a prime mover, an output torque of the engine is varied inevitably. In addition, a torque transmitting capacity of a friction clutch is also varied inevitably. For these reasons, if the torque compensating rate is set to a constant value determined based on a result of experimentation, the torque may not be controlled accurately taking account of variations in the engine torque and the torque transmitting capacity of the clutch, and hence a drop in the drive force and a resultant shock may not be reduced sufficiently. In addition, the controller taught by JP-A-2010-115983 is configured to reduce the torque compensating rate before learning the timing of torque compensation sufficiently. However, although the past data can be reflected on such learning control, the current situation cannot be reflected on the learning control. In addition, such reduction in the torque compensating rate may not be always effective before learning the timing of torque compensation sufficiently. For this reason, the conventional learning control of the timing of torque compensation may be improved to reduce drop in driving force and shocks.
The torque compensation by the engine torque taught by JP-A-2010-115983 may be effective to reduce drop in drive force and shocks during execution of the clutch-to-clutch shifting. However, the controller taught by JP-A-2007-239832 thus configured to adjust the engine speed to the target speed by the feedback method cannot be used to reduce drop in drive force and shocks during execution of the clutch-to-clutch shifting. Meanwhile, the shift control device taught by JP-A-2001-124196 is configured to control engine torque during execution of the power-on downshifting and hence the shift control device taught by JP-A-2001-124196 cannot be used to control the engine torque during execution of upshifting. In addition, according to the teachings of JP-A-2001-124196, deficiency and shortage of energy during execution of the shifting operation is corrected by the engine torque. According to the teachings of JP-A-2001-124196, therefore, the input speed may be adjusted to the target speed, but drop in drive force and shocks in the torque phase during execution of upshifting may not be reduced.